RFC 6653
DHCPv6 Prefix Delegation in Long-Term Evolution (LTE) Networks
RFC 6653: DHCPv6 Prefix Delegation in Long-Term Evolution (LTE) Networks 🎀
Okay bestie, here's the vibe check 💖 This is RFC 6653, and it's an Independent Submission with the category Informational. Its ISSN is 2070-1721 and it's dated July 2012. The authors are B. Sarikaya, F. Xia (both from Huawei USA) and T. Lemon (from Nominum). It doesn't obsolete or update any other RFCs, since the header doesn't list any. 🦋
Abstract ✨
As everyone gets obsessed with IPv6 showing up in cellular networks, a bunch of migration issues keep popping up, and this doc is all about IPv6 prefix management 🌸 The big idea is that DHCPv6 servers can manage prefixes, so we use DHCPv6 Prefix Delegation to let an access router offload prefix delegation and release tasks to a DHCPv6 server 💅 The access router first requests a prefix for an incoming mobile node from the DHCPv6 server. Then the access router may do stateless or stateful address allocation for the mobile node, e.g., with a Router Advertisement or using DHCP. We also describe prefix management using Authentication, Authorization, and Accounting (AAA) servers. It's giving thorough 🧚
Status of This Memo 🌈
This document is not an Internet Standards Track specification. It's published for informational purposes ✨
This is a contribution to the RFC Series, independent of any other RFC stream. The RFC Editor chose to publish this document at its discretion, and they make no statement about its value for implementation or deployment. Documents approved for publication by the RFC Editor are not a candidate for any level of Internet Standard, see Section 2 of RFC 5741 🫶
Information about the current status of this document, any errata, and how to give feedback on it can be found at http://www.rfc-editor.org/info/rfc6653 💜
Copyright Notice 💖
Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. 🎀
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, because they describe your rights and restrictions with respect to this document 🙈
Table of Contents 🍓
1. Introduction ....................................................3
2. Terminology and Acronyms ........................................4
3. Prefix Delegation Using DHCPv6 ..................................5
3.1. Prefix Request Procedure for Stateless Address
Configuration ..............................................5
3.2. Prefix Request Procedure for Stateful Address
Configuration ..............................................7
3.3. The MN as Requesting Router in Prefix Delegation ...........8
3.4. Prefix Release Procedure ...................................9
3.5. Miscellaneous Considerations ...............................9
3.5.1. How to Generate an IAID .............................9
3.5.2. Policy to Delegate Prefixes ........................10
4. Prefix Delegation Using RADIUS and Diameter ....................10
5. Security Considerations ........................................11
6. Acknowledgements ...............................................12
7. Informative References .........................................121. Introduction ✨
Figure 1 is the cute diagram that shows the key elements of a typical cellular access network 🦋 In a Long-Term Evolution (LTE) network, the Access Router (AR) is the Packet Data Network (PDN) Gateway [3GPP-23401].
+-------------+
| +------+ |
| |DHCP | |
+-----+ +-----+ +------+ +------+ | |Server| | +------+
| MN |--| BS |--+Access+--+Access+-+ +------+ +-+Border|
+-----+ +-----+ | GW | |Router| |IP Network(s)| |Router+-Internet
+--+---+ +--+---+ | | +------+
| | +-------------+
+-----+ +-----+ | | +------+
| MN |--| BS |-----+ | |AAA |
+-----+ +-----+ +--- |Server|
+------+Figure 1: Key Elements of a Typical Cellular Network
The Mobile Node (MN) attaches to a Base Station (BS) through an LTE air interface 📱 A BS manages connectivity of User Equipment (UE) and extends connections to an Access Gateway (GW), e.g., the Serving Gateway (S-GW) in an LTE network. The access GW and the AR are connected through an IP network. The AR is the first-hop router for the MNs, and it's in charge of address/prefix management 👑
The AR is connected to an IP network owned by the operator, and that network connects to the public Internet through a border router 🌐 The network also has servers for subscriber management, which covers Quality of Service, billing, and accounting, plus a Dynamic Host Configuration Protocol (DHCP) server [RFC6342] ✨
With IPv6 addressing, mobile network links are point-to-point (P2P), so the per-MN interface prefix model is used [RFC3314] [RFC3316]. In the per-MN interface prefix model, prefix management is an issue 💅
Here's the lifecycle. When an MN attaches to an AR, the AR requests one or more prefixes for the MN. When the MN detaches from the AR, the prefixes should be released. When the MN becomes idle, the AR should keep (i.e., not release) the allocated prefixes 🥺
This document describes how to use DHCPv6 Prefix Delegation (DHCPv6-PD) in mobile networks, such as networks based on standards from the 3rd Generation Partnership Project (3GPP). It could also easily be adopted by the Worldwide Interoperability for Microwave Access (WiMAX) Forum 🌸 With the migration to IPv6, the number of MNs connected to the network at a given time may get very high. Traditional techniques like prefix pools are not scalable, so in those cases DHCPv6-PD is the viable approach to take 💜
The techniques described in this document have not been approved by the IETF or the 3GPP, except for the techniques described below in Section 3.3. This document is not a Standard or a Best Current Practice. It's published only for possible consideration by operators 🙈
This document is useful when address space needs to be managed by DHCPv6-PD. Obviously there are other ways to manage address space, including having the AR track internally which address space is used by which mobile 🧚
2. Terminology and Acronyms 🌸
- 3GPP - 3rd Generation Partnership Project
- AAA - Authentication, Authorization, and Accounting
- AR - Access Router
- BS - Base Station
- DHCP - Dynamic Host Configuration Protocol
- E-UTRAN - Evolved Universal Terrestrial Radio Access Network
- GPRS - General Packet Radio Service
- LTE - Long-Term Evolution
- MN - Mobile Node
- P2P - Point-to-Point
- PD - Prefix Delegation
- PDN - Packet Data Network
- S-GW - Serving Gateway
- WiMAX - Worldwide Interoperability for Microwave Access
3. Prefix Delegation Using DHCPv6 💅
"Access router" refers to the cellular network entity that has a DHCP client 🫶 According to [3GPP-23401], the DHCP client is located in the PDN Gateway, so the AR is the PDN Gateway in the LTE architecture 🎀
3.1. Prefix Request Procedure for Stateless Address Configuration ✨
okay so there are two function modules in the AR: the DHCP client and the DHCP relay 🧚. DHCP messages should be relayed if the AR and a DHCP server aren't directly connected. otherwise the DHCP relay function in the AR is not necessary 💅. here's what it looks like when they're NOT directly connected:
+-------+ +----------------------+ +-----------+
| MN | | AR | |DHCP Server|
+-------+ |DHCP | Relay | +-----------+
| |Client | Agent | |
| +----------------------+ |
|1 Initial NW entry | |
|or attach procedure| |
|<----------------->| |
| |2 Solicit |
| |---------> Relay-forward |
| | --------------->|
| | 3 Relay-reply |
| |Advertise <---------------|
| |<-------- |
| |4 Request |
| |---------> Relay-forward |
| | --------------->|
| | 5 Relay-reply |
| |Reply <---------------|
| |<-------- |
|6 Attach | |
| Completed | |
|<----------------->| |
|7 Router | |
| Solicitation | |
|------------------>| |
| 8 Router | |
| Advertisement | |
|<------------------| |Figure 2: Prefix Request 🎀
- so an MN (also called UE, or User Equipment, by the 3GPP 📱) does its initial network entry and authentication, a.k.a. the attach procedure 🔐.
- once Step 1 is done successfully, the AR kicks off the DHCP Solicit procedure to ask for prefixes for the MN 🙌. the DHCP client in the AR creates and sends a Solicit message the way Sections 17.1.1 ("Creation of Solicit Messages") and 17.1.2 ("Transmission of Solicit Messages") of [RFC3315] describe. the DHCP client in an AR that supports DHCPv6 Prefix Delegation [RFC3633] creates an Identity Association for Prefix Delegation (
IA_PD) and gives it an Identity Association IDentifier (IAID) 🆔. the client must include theIA_PDoption in the Solicit message. the DHCP client as Requesting Router (RR) must set theprefix-lengthfield to a value less than, e.g., 48 or equal to 64 to request a /64 prefix 🍓. next, the relay agent in the AR sends a Relay-forward message to the DHCP server, and the Solicit message is encapsulated inside it 📦. - the DHCP server sends an Advertise message to the AR the same way Section 17.2.2 ("Creation and Transmission of Advertise Messages") of [RFC3315] describes ✨. an Advertise message with the
IA_PDshows that the DHCP server is capable of delegating prefixes 👑. the relay agent in the AR gets this encapsulated in a Relay-reply message, and then it's sent to the DHCP client in the AR as an Advertise message 💌. - the AR (DHCP client and relay agent) uses the same message exchanges as Section 18 ("DHCP Client-Initiated Configuration Exchange") of [RFC3315] and [RFC3633] describe, to get or update prefixes from the DHCP server 🔄. the AR (DHCP client and relay agent) and the DHCP server use the
IA_PDPrefix option to swap info about prefixes, kinda like how IA Address options are used for assigned addresses 🫶. this happens when the AR sends a DHCP Request message and the DHCP server sends back a DHCP Reply message 💜. - the AR stores the prefix info it got in the Reply message 📝.
- a connection between the MN and the AR gets set up, and the link becomes active 🌈. this step finishes the Packet Data Protocol (PDP) Context Activation Procedure in Universal Mobile Telecommunications System (UMTS) and PDN connection establishment in LTE networks 📶.
- the MN may send a Router Solicitation message to ask the AR to send a Router Advertisement (RA) message 🙋.
- the AR advertises the prefixes it got in the
IA_PDoption to the MN via an RA, once the PDP Context/PDN connection is established, or when it responds to a Router Solicitation message from the MN 📣.
the 4-way exchange between the AR as RR and the DHCP server as Delegating Router (DR), like in Figure 2, can be cut down to a two-message exchange by using the Rapid Commit option [RFC3315] ⚡. the DHCP client in the AR acting as RR includes a Rapid Commit option in the Solicit message, and then the DR sends a Reply message with one or more prefixes 🦋.
3.2. Prefix Request Procedure for Stateful Address Configuration 🌸
stateful address configuration needs a different setup than the one in Figure 2 🙈. in this kind of configuration there are two function modules in the AR: the DHCP server and the DHCP client 💅.
after the initial attach is done, a connection to the AR gets set up for the MN 🔗. the DHCP client function at the AR as RR and the DHCP server as DR follow Steps 2 through 5 of the procedure in Figure 2 to get the new prefix for this interface of the MN, using the IA_PD option exchange defined in [RFC3633] 🎁.
the DHCPv6 client at the MN sends the DHCP Request to the AR 📨. the DHCP server function at the AR must use the IA_PD option it got in the DHCPv6-PD exchange to assign an address to the MN 🏠. the IA_PD option must contain the prefix 💖. the AR sends a DHCP Reply message to the MN with the IA address option (IAADDR) in it 📬. Figure 3 shows the message sequence 👀.
the MN configures its interface with the address the DHCP server gave it in the DHCP Reply message 🎀.
in Figure 3, the AR may be the home gateway of a fixed network that the MN connects to during the MN's handover 🏡.
+----------+ +--------------+ +-----------+
| MN | | AR | |DHCP Server|
| |DHCP | | DHCP |DHCP | +-----------+
| |Client| |Server|Client |
+----------+ +--------------+
| Initial NW entry | |
|or attach procedure | |
|<-----------------> | |
| | DHCPv6-PD exchange |
| | similar to Steps 2-5 |
| Solicit | of Figure 2 (IA_PD) |
|---------------------->| |
| Advertise | |
|<----------------------| |
| Request | |
|---------------------->| |
| | |
| | |
| | Use prefix in IA_PD |
| Reply | to assign IAADDR |
|<--------------------- | |Figure 3: Stateful Address Configuration Following PD 🧁
3.3. The MN as Requesting Router in Prefix Delegation 👑
the AR may use a DHCPv6 Prefix Delegation exchange to get a delegated prefix shorter than /64, by setting the prefix-length field to a value less than 64, e.g., 56 to get a /56 prefix 🌈. each newly attaching MN first goes through the steps in Figure 2, where the AR asks for a shorter prefix to set up a default connection with the MN 🔌.
the MN may then ask the AR for more prefixes (/64 or shorter) using DHCPv6 Prefix Delegation, where the MN is the RR and the AR is the DR (see [RFC6459] and Section 5.3.1.2.6 of [3GPP-23401]) 🛰️. in this case the call flow looks a lot like Figure 3 💫. the Solicit message must include the IA_PD option with the prefix-length field set to 64 🍬. the MN may request more than one /64 prefix 🍓. the AR as DR must delegate these prefixes, excluding the prefix assigned to the default connection 🙅♀️.
3.4. Prefix Release Procedure 🦋
prefixes can be released in two ways: through prefix aging, or through the DHCP release procedure 🌷. with prefix aging, a prefix should not be used by an MN when it ages, and the DHCP server can then delegate it to another MN ⏳. the prefix lifetime gets delivered from the DHCPv6 server to the MN via the DHCP IA_PD Prefix option [RFC3633] and the RA Prefix Information option [RFC4861] 📜. Figure 4 shows how the AR releases prefixes to a DHCP server that isn't directly connected to the AR 🚀:
- a signal that an MN has detached, like a switch-off or handover, kicks off the prefix release procedure 🔚.
- the AR starts a Release message to give the prefixes back to the DHCP server 🔙.
- the server responds with a Reply message 💌. the prefixes can then be reused by other MNs ♻️.
+-------+ +-------+ +-----------+
| MN | | AR | |DHCP Server|
+-------+ +-------+ +-----------+
| | |
| 1 De-registration | |
| handover, or other | |
|<--------------------->| |
| |2 Relay-forward/Release|
| |---------------------->|
| | |
| |3 Relay-reply/Reply |
| |<--------------------- |
| | |
| | |Figure 4: Prefix Release 💅
3.5. Miscellaneous Considerations 🧚
3.5.1. How to Generate an IAID
okay so the IAID is 4 bytes in length 🎀 and it should be unique in the scope of an AR. the prefix table should be maintained 📒. this table holds the IAID, the Media Access Control (MAC) address, and the prefix(es) assigned to the MN. in LTE networks, the International Mobile Equipment Identity (IMEI) uniquely identifies the MN's interface, so it corresponds to the MAC address 🔑. the MAC address of the interface should be stored in the prefix table, and it's used as the key for searching the table 🔍.
the IAID should be set to Start_IAID, and Start_IAID is an integer of 4 octets ✨. this is the algorithm used to generate the IAID, and it's giving very step-by-step energy:
- Set this IAID value in the
IA_PD Prefixoption. Request a prefix for this MN as described in Section 3.1 or Section 3.2. - Store the IAID, MAC address, and received prefix(es) in the next entry of the prefix table.
- Increment the IAID.
a prefix table entry for an MN that hands over to another AR must be removed 🙅♀️. then the IAID value is released and can be reused 🔁. iconic recycling, honestly 💅
3.5.2. Policy to Delegate Prefixes
okay, this one's about P2P links 🛣️. if /64 prefixes of all MNs connected to one or more ARs get broadcast dynamically upstream as route information, you'll get high routing-protocol traffic (IGP, OSPF, etc.) because of the per-MN interface prefixes 😭. that's a whole mess, so there are two solutions 👑.
solution one is static configuration, which would be preferable in many cases 🧚. no routing protocols are needed, because each AR has a known piece of address space. if the DHCP servers also know that address space, then they will assign a particular AR a prefix from that space 🍓.
solution two is route aggregation 🌈. for example, each AR can be assigned a /48 or /32 prefix (an aggregate prefix, a.k.a service provider common prefix), while each interface of an MN can be assigned a /64 prefix. the /64 prefix is an extension of the /48 prefix. for example, an AR's /48 prefix is 2001:db8:0::/48, while an interface of the MN is assigned 2001:db8:0:2::/64. the border router in Figure 1 may be manually configured to broadcast only an individual AR's /48 or /32 prefix information to the Internet 🦋
4. Prefix Delegation Using RADIUS and Diameter ✨
in the initial network entry procedure shown in Figure 2, the AR as Remote Authentication Dial In User Service (RADIUS) client sends an Access-Request message with MN information to the RADIUS server 📨. if the MN passes authentication, the RADIUS server may send an Access-Accept message with prefix information to the AR using the Framed-IPv6-Prefix attribute. the AAA server also provides routing information to be configured for the MN on the AR, using the Framed-IPv6-Route attribute 🗺️. so the AR can handle initial prefix assignments to MNs, but managing the lifetime of the prefixes is totally left to the AR 🫠. the Framed-IPv6-Prefix is not designed to support delegation of IPv6 prefixes, so for this situation, the Delegated-IPv6-Prefix attribute (discussed below) can be used 💜.
[RFC4818] defines a RADIUS attribute, Delegated-IPv6-Prefix, which carries an IPv6 prefix to be delegated. this attribute is usable within either RADIUS or Diameter. [RFC4818] recommends that the DR use the AAA server to receive the prefixes to be delegated, by using the Delegated-IPv6-Prefix attribute/Attribute-Value Pair (AVP) 🎀.
the DHCP server as DR, as shown in Figure 2, may send an Access-Request packet containing the Delegated-IPv6-Prefix attribute to the RADIUS server to request prefixes 🙏. in the Access-Request message, the DR may provide a hint that it would prefer a prefix -- for example, a /48 prefix. as the RADIUS server is not required to honor the hint, the server may delegate a longer prefix -- e.g., /56 or /64 -- in an Access-Accept message containing the Delegated-IPv6-Prefix attribute [RFC4818]. the attribute can appear multiple times when the RADIUS server delegates multiple prefixes to the DR. the DR sends the prefixes to the RR using the IA_PD option, and the AR as RR uses them for MNs, as described in Section 3 🌸
when Diameter is used, the DHCP server as DR, as shown in Figure 2, sends an AA-Request message 📬. the AA-Request message may contain a Delegated-IPv6-Prefix AVP. the Diameter server replies with an AA-Answer message, which may contain a Delegated-IPv6-Prefix AVP. the AVP can appear multiple times when the Diameter server assigns multiple prefixes to an MN 🧁. the Delegated-IPv6-Prefix AVP may appear in an AA-Request packet as a hint from the AR to the Diameter server that it would prefer a prefix -- for example, a /48 prefix. the Diameter server may delegate, in the AA-Answer message, a /64 prefix, which is an extension of the /48 prefix 🌟. as in the case of RADIUS, the DR sends the prefixes to the RR using the IA_PD option, and the AR as RR uses them for the MNs as described in Section 3 🫶
5. Security Considerations 🚨
okay bestie, this part is SERIOUS, so read carefully 🙈. this document does not introduce any additional message types, and therefore it does not introduce any additional threats 🛡️. the security procedures for DHCPv6 [RFC3633], RADIUS [RFC2865], and Diameter [RFC3588] apply. so the whole security story is the stuff those specs already cover, and nothing new got added here 💀
6. Acknowledgements 💖
we are so grateful to Suresh Krishnan, Hemant Singh, Qiang Zhao, Ole Troan, Qin Wu, Jouni Korhonen, Cameron Byrne, Brian Carpenter, Jari Arkko, and Jason Lin 🥹. their in-depth reviews of this document led to several improvements, and honestly they're the real MVPs 👑
7. Informative References 📚
here are all the references, copied exactly 🦋
[3GPP-23401]
3GPP, "General Packet Radio Service (GPRS) enhancements
for Evolved Universal Terrestrial Radio Access Network
(E-UTRAN) access (Release 11)", TS 23.401 V11.0.0,
December 2011.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
[RFC3314] Wasserman, M., "Recommendations for IPv6 in Third
Generation Partnership Project (3GPP) Standards",
RFC 3314, September 2002.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3316] Arkko, J., Kuijpers, G., Soliman, H., Loughney, J., and J.
Wiljakka, "Internet Protocol Version 6 (IPv6) for Some
Second and Third Generation Cellular Hosts", RFC 3316,
April 2003.
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC4818] Salowey, J. and R. Droms, "RADIUS Delegated-IPv6-Prefix
Attribute", RFC 4818, April 2007.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC6342] Koodli, R., "Mobile Networks Considerations for IPv6
Deployment", RFC 6342, August 2011.
[RFC6459] Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,
T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
Partnership Project (3GPP) Evolved Packet System (EPS)",
RFC 6459, January 2012.Authors' Addresses 🦋
Behcet Sarikaya
Huawei USA
5340 Legacy Dr.
Plano, TX 75074
EMail: sarikaya@ieee.org
Frank Xia
Huawei USA
1700 Alma Drive, Suite 500
Plano, TX 75075
Phone: +1 972-509-5599
EMail: xiayangsong@huawei.com
Ted Lemon
Nominum
2000 Seaport Blvd.
Redwood City, CA 94063
EMail: mellon@nominum.com📦 where this page comes from
- ietf: rfc6653 2012-07
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms